Adjustable curve ruler



Jan. 10, 1933. w. s. WESTON -1,893,689

, ADJUSTABLE CURVE RULER Filed Jan. 13, 1930 2 Sheefts-SheeJ 1 Jan. 10, 1933.

w. s. WESTQN ADJUSTABLE CURVE RULER Filed Jan. 15, 1950 2 Sheets-Sheet Fig. 4-

v Tm Q 0 a. I 2- PO \A 5 O R y n. m b w J Inventor:

WM f M by m/v4 Patented Jan. 10, 1933 ATENT F ICE WILLIAM S. WESTON, '03: DALLAS, TEXAS ADJUSTABLE CURVE RULER Application fi1ed.J'anuary 13, 1930. Serial No. 420,474.

of an ordinary drafting compass, or beam compass, is impracticable. It comprises a flexible arm member of constant length; rigid end frames or members attached to the ends of'the arc member and provided with edges or other means for indicating or defining lines that are tangent and radial respectively to the arc member; and links pivotally connecting the rigid end frames and arranged to hold the ends or tangent points of the flexible arc member at the correct distance apart and the tangent and radial line indicating means in correct relation to the arc member when the latter is flexed to any desiredradius. The invention is hereinafter more fully described, illustrated in its preferredembodiment in the accompanying drawings, and more particularly pointed out in the appended claims.

Referring to the drawings:

Fig. 1 is a plan View of the improved curve ruler with the arc member in the straight line position; that is, the position for a radius of infinite length.

Figs. 2 and 3 are similar views with the arc member flexed through. angles of 90 and 180 degrees respectively.

Figs. 4, 5 and 6 are plan, side and end views of the left hand end frame.

Fig. 7 is ageometric illustration showing the relative location, dimensions and spacing of the parts used in the design of the instrument illustrated in Figs. 1, 2 and 3..

Fig. 8 is a similar view of a modification.

The are member A is made of a ribbon of spring steel or other highly resilient material having a uniform elastic quality throughout its length. To attach the arc member to the end frames, F and F the ribbon is extended at each end through a. slot B, Fig. 5,

" in the bottom of each end frame where it is securely held in place either by soldering or by any other practicable means. The points where the ribbon enters the slots are the ends or tangent points of the arc and are designated,in accordance with the common practice of engineers and draftsmen, as PC, point of curve, and PT, point of tangent, both terms being interchangeable-and used to distinguish one end of a curve from the other. The end portions T of the ribbon extending through and beyond the slots, remain straight, being attached to the frames, and provide means for indicating tangents to the arc portion at PC and PT. The inside edges of the end; frames, marked R, at right angles to the slots so B, intersect the tangents at the points PG and PT and therefore define or indicate radial lines for the curve at those points. The lower or bottom faces of the end frames and the lower edge of the arc member A lie (15 in thesame plane'and rest on any flat surface upon which the instrument is placed. Since the arc member A consists only of a ribbon of steel and is not much thicker than an ordinary ruled line, it is preferably illus- {rated in Figs. 1,. 2 and 3 by a heavy, dark When the arc portion of the instrument is flexed from a straight line to a curve of any i desired radius, the ends or tangent points of, the curve, PC and PT, are necessarily brought closer together and. the end frames rotated relative to each other through an angle equal to that subtended by the arc. To insure the flexing of the ruler member A in an are of uniform curvature, the end frames, as they are rotated, should be maintained in correct relation and the ends or tangent points of the arc member should be'positi'oned -'i the correct distance apart for any given curve, independently of the internal strains in the flexibleporti0n of the arc member. For this purpose, rigid bars or links D and E are pivotally connected to the end frames and disposed in crossed relation to each other so that any relative movement of the frames to or from each other is attendedwith. a relative rotative movement in opposite directions, Such connections insure that, when the PC and PT of the arc portion are the correct distance apart for any given curve, the tangent and radial lines indicated or defined by the end frames will also be in correct relation to such curve. With the PC and PT and the tangent and radial lines thus held in correct relation, independent of the arc member, the uniform resilience of that member may be depended upon to hold its curvature uniform to the radius desired sufficiently 5 close for all practical uses of the instrument in the drawing or checking of curves.

In the preferred construction, the frames are each provided with a pair of inwardly projecting arms on opposite sides of the are member, and the bar or link D connects a pivot 0 on the outside arm of the left-hand frame with the pivot I on an inside arm of the right-hand frame, while the bar E connects the outside pivot 0 of the righthand frame to the inside pivot I of the left-hand frame. The dimensions of the end frames and of the connecting bars are the same except that they are symmetrically oppositely arranged as rights and lefts.

While the bars D and E could be straight, following the line connecting their respective pivot points, as illustrated geometrically in Fig. 7 they are preferably provided with goose-neck bends as shown. When so shaped, they cross each other inside of the arc member and do not cross any portion of the flexible arc member and hence do not interfere with drafting operations as would be the case with straight connections. Also, the curved portion of one of the bars can be provided with a scale as shown, to facilitate the adjustment of the arc member to any desired angle of curvature or any desired radius. Again, as shown, the curved portion of each bar is also concentric with its outside pivot point 0 or 0 and is maintained at constant distance from that point. Hence, clamp screws S on the frames can be employed for securing the bars and frames against relative move ment and thus holding the parts in position corresponding to any desired angle or degree of curvature.

While in the preferred construction a clamp screw is provided on both end frames, yet, for most uses, particularly for all curves between those of Figs. 1 and 2, one screw would be sufficient to clamp the instrument to any desired adjustment. For example, if the screw on the left-hand frame is clamped, then three of the pivot points, 0 I and 1,, will be held in fixed relation, and the fourth point 0 cannot be moved without a distortion of the connecting bars or the end frames. Only for adjustments near that of Fig. 3, where the four pivot points are in line, could the pivot point 0 be moved with a minimum of distortion, assuming the pivots to be tight and free of lost motion.

60 Referring now to the eometric Fig. 7,

With the length of the are i l from PC to PT taken as 7.854, the distarcc between the outside pivot point at one end and the inside pivot point at the other end is 5.0. The location of the pivot points relative to the PC or PT and relative to the tangent line T and radial line R for the above dimensions are as shown. Point O and point I relative to the tangent line extended, which is the straight line position of the arc portion, are outside and inside respectively of that line the same distance, 0.775 as shown. These points are also the same distance from the radial line extended through the PC or PT, 1.550, as shown. The instrument as illustrated built to these dimensions, is designed for arcs of all angles up to 180 degrees and the relative dimensions are correct to a small fraction, plus or minus, in the third decimal place, and sufliciently close for all practical uses.

Vith an are 7 .854 long subtending an angle of degrees as illustrated in Fig. 2, the radius of the arc would be 5.0, as can be figured trigometrically by the combination of the arc length and the angle. In Fig. 3, with an arc of 180 degrees, the radius is 2.5, which can be figured in the same way from the arc length and angle, or more directly interpreted as one-half the radius of the arc of one-half the angle. Because of this coordinate relation between the radius and the angle subtended by the are, I have preferably provided a scale of angles on bar D over the lefthand end frame. The fineness of the division in this scale depends upon the size of the instrument. The instrument may be made with an arc of any length, for example, 15.708. In that case the other dimensions given in Fig. 7 would be increased in the same proportion.

In Fig. 3 it will be noted that when the ribbon of steel or other resilient material is curved to the arc of 180 degrees, it will en croach on the arms of the end frames carrying the inside pivot points. The instrument will seldom be used for curves of the small radii near the 180 degree angle, yet to provide for such use the lower portion ofthe arms carrying points I and I is cut aw to clear the arc ribbon, as indicated at I in Figs. 4: and 5. In the particular form shown, as indicated in Fig. 3, the frames F and F are adapted to abut in this extreme position.

In the manufacture of the instrument, after the length of the arc member has been decided upon, in either the English or metric or any other system of measurements, a scale may be inscribed on the right-hand connecting bar E, giving the length of the radius direct. However, whatever system may be used, with the length of the arc in terms of that system known, the angle on the lefthand scale may be used to set or determine the radius.

It is to be noted that the length of the are A, which is constant for all angles of curvature, is necessarily measured along the center line of the steel ribbon forming the arc. In the use of the instrument either side of the ribbon may be used as the ruling edge. The radius of the line drawn outside the are is a trifle longer and the radius of the line inside the arc a trifle shorter than the theoretical radius determined from the angle of the scale-a variation that is of immaterial importance in the general use of the instrument.

It is to be noted also that a scale on the instrument is not absolutely essential. The instrument may be adjusted to a curve of any radius shown on a diagram of curves.

The instrument also may be used as a protractor for checln'ng or laying out angles, the angle indicated on the scale being the angle between the tangents defined by the edges T or between the radial lines defined by ed es B when extended to an intersection. or this use the outer ends of the frames defining the tangents may be made longer in proportion than shown in the drawings.

It is particularly noted that. as shown diagrammatically in Fig. 8, it is possible and practical in the manufacture of the improved instrument, to vary the location of the pivots of the connecting links by which two points on one end frame are paired with and held at constant distance in diagonal relation to two points respectively on the other end frame. In the arrangement illustrated in this figure, with the are 7854 long, the paired outside pivot point at one end and inside pivot point at the other end are so located that the straight distance between them is 4.5. For these dimensions the distances of the pivot points from the tangent and radial lines are as shown in the figure. These dimensions are correct to a small fraction in the third decimal place, the same as stated in Fig. 7.

My present invention is based on the fact that in an adjustable are ruler having a flexible curve member with rigid frame members fixed at its ends to provide tangent and radial lines, there are a series of points in fixed position relative to one end frame of the instrument, each of which remains at constant distance each from a different point in a series of points that are in fixed position relative to the other end frame. Any two points, one in fixed relation to one end frame and one in fixed relation to the other end frame, that remain at constant distance from each other, constitute one of the pairs of points referred to in the specifications and in the claims. By utilizing this fact, I can pivotally connect one end frame with the other in a manner to hold both frames in correct relation for the arc to which the flexible member may be curved, independent of that member. It will be noted that the link arrangement disclosed adjustably connects the end frames while also serving to maintain the same symmetrically disposed relative to a radial line bisecting the flexible arc member or to a chord of the arc defined thereby. In this construction, the lengths of the consame distance relation.

construction of the instrument, I may use the relative distance between points O and S1 necting links are determined by the constant distances between at least two .pairs of cthe points above described.

It is to be noted that the two pairs of points-selected need not necessarily have the For example, in the of Figure 7 in combination with'the relative distance between points 1 andO 'of Figure 8 to determine the lengths of the links in Figures 1, 2 and 3.

Changes'may be made in the detailsset forth without departure from the scope of the invention as defined in the appended claims.

I claim as my invention:

1. An adjustable curve ruler comprisinga flexible are member of constant length, rigid frame members attached tothe ends of the .arc member and having means indicating 'otally connected at opposite ends to said end members for maintaining the ends of the arc member at the correct distance apart andthe tangent and radial line indicating means in correct relation thereto as the arc member is flexed to any desired radius.

2. An adjustable curve ruler comprising an arc member having a flexible portion of constant length, rigid frame members attached to the ends of the arc member, and means for holding two points on oneend frame paired with and at constant distance from two points on the other end frame respectively.

8. A combined curve ruler and protractor comprising a flexible arc member of constant length, a pair of rigid end members attached to the ends of said are member and having edges disposed tangent and radial, respectively, to the arc member at its ends, and two crossedlinks of constant length, each pivotally connecting a point on one end member with a point on the other end member for automatically causing the end members to assume, throughout the range of adjustment of the device, a symmetrical position relative to a radial line bisecting the flexible are member.

4. An instrument of the class described comprising end frames, a flexible arc member immovably secured to said end frames, and link connections of constant length between the frames respectively connecting and holding a point outside and adjacent each end of the arc member at a constant distance from a point inside and adjacent the opposite end thereof, said points at each end being in fixed relation to each other and the adjacent end of the arc member.

5. A curve ruler comprising a flexible arc member, rigid frames secured to the end of said flexible member and having edges tangent and radial respectively to said are member and intersecting at the tangent points thereof, and crossed connecting links pivoted to said frames and arranged to maintain the tangent points of said arc member at the correct distance apart and said tangent and radial edges in correct relation to the are member when the latter is flexed to the desired radius.

6. A curve ruler comprising end frames having laterally projecting outer and inner arms, a flexible arc member connected at its ends to said frame at points between the arms thereof, and a pair of crossed links, each pivoted to the outer arm of one frame and to the inner arm of the other frame, said links having bent portions extending about theends of said flexible member.

7. A curve ruler comprising rigid end frames, a flexible arc member extending between said frames, the latter having project-- ing arms on opposite sides of the end portions of said are member, and crossed links pivoted to said arms, at least one of said links having an end portion concentric with the pivot point at such end.

' WVILLIAM S. XVESTON. 

